The Fox and the Sour Grapes

Illustrating the origin of what sour grapes are (post-Aesop, that is), Crow gets Fox to trade him his picnic lunch for some grapes high on a vine. After many difficulties, the fox manages to get to them but discovers they are sour indeed.
Chuck Jones later acknowledged this short as one of the inspirations for his popular Road Runner cartoons.

Plot summary: IMDb